Oligonucleotides matching COL7A1 exon 73 for epidermolysis bullosa therapy

ABSTRACT

Antisense oligonucleotides capable of preventing or reducing exon 73 inclusion into the human COL7A mRNA are characterized in various ways: (a) the oligonucleotide&#39;s sequence includes at most two CpG sequences; (b) the oligonucleotide has a length of no more than 24 nucleotides; (c) the oligonucleotide is capable of annealing to the (SRp40/SC35 binding/ESE) element in exon73. These oligonucleotides can usefully be oligoribonucleotides with modified internucleosidic linkages e.g. phosphorothioate linkages.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/554,420, filed on Aug. 29, 2017 which is a § 371 national phase ofInternational Application No. PCT/EP2016/055360, filed on Mar. 11, 2016,which claims the benefit of United Kingdom patent application 1504124.7,filed Mar. 11, 2015, the complete contents of which are herebyincorporated herein by reference for all purposes.

SEQUENCE LISTING

The instant application contains a Sequence Listing which has beensubmitted in ASCII format via EFS-Web and is hereby incorporated byreference in its entirety. The ASCII copy, created on Dec. 4, 2017, isnamed PQR-006_SL.txt and is 15,185 bytes in size.

FIELD OF THE INVENTION

The present invention is concerned with oligonucleotides suitable foruse in treating human disease. More in particular the present inventionis concerned with antisense oligonucleotides suitable for the treatmentof dystrophic epidermolysis bullosa.

DISEASE BACKGROUND

Epidermolysis Bullosa (EB) is a group of heritable skin diseases, whichare characterized by chronic fragility and blistering of the skin andmucous membranes. Depending on the subtype, the spectrum of symptoms ofthe EB is very broad, ranging from minimal skin fragility to very severesymptoms with general complications. Worldwide about 350,000 patientsare affected. In some forms of EB, also nails, hair and teeth may beinvolved. The main types of EB include EB Simplex (EBS), Junctional EB(JEB), Dystrophic EB (DEB) and Kindler syndrome (KS).

DEB affects about 25% of EB patients, can be either dominantly orrecessively inherited, and involves defects in Type VII collagen(COL7A1, omim 120120). COL7A1 encoding the alpha-1 chain of collagenVII. Collagen VII functions as an anchoring fibril of the upper part ofthe dermis to the lamina densa (part of the basement membrane).Following post-translational modification three identical alpha-1 chainsfold together with their collagenous triple helix domain. Subsequently,antiparallel dimers are formed that align to form the anchoring fibrils.Collagen VII is synthesized in the skin by keratinocytes and dermalfibroblasts. DEB disease severity roughly correlates with the amount oftype VII collagen expression at the basement membrane zone.

Characteristics of Dominant Dystrophic EB (DDEB) include blistering thatmay be localized to the hands, feet, elbows and knees or generalized.Common findings include scarring, milia, mucous membrane involvement,and abnormal or absent nails. Recessive Dystrophic EB (RDEB) istypically more generalized and severe than DDEB. In addition to thefindings of DDEB, other common manifestations of RDEB includemalnutrition, anemia, osteoporosis, esophageal strictures, growthretardation, webbing, or fusion of the fingers and toes causing mittendeformity (pseudosyndactyly), development of muscle contractures,malformation of teeth, microstomia and scarring of the eye. The risk ofsquamous cell carcinoma is greatly increased in this group as well asdeath from metastatic squamous cell carcinoma.

Within the gene COL7A1 more than 400 different mutations are known. Oneof the most prevalent affected exons (18% of patients) is exon 73 withabout 40 known mutations, most often missense mutations or mutationsleading to premature termination codons (PTCs) and glycinesubstitutions. Currently there is no treatment for DEB, only palliativecare is performed. Severe forms of RDEB impose a high cost on society'shealthcare budget: the average costs of dressings and medication isabout €200,000 per patient per year.

WO2013/053819 of Institut National de la Sante et de la RechercheMédicale (INSERM) discloses two antisense oligonucleotides targetingexon 73, causing the entire exon to be skipped from the mRNA. Theexon-73-deficient mRNA is translated into a functional polypeptide that,although being shorter than the wt protein, behaves very similar towild-type collagen Vila. One oligonucleotide disclosed is 25 nucleotidesin length, displaying a skipping efficiency of 69%, while the other is30 nucleotides in length, displaying 93% skipping efficiency.

SUMMARY OF THE INVENTION

Although the longer exon-skipping AON in WO2013/053819 appears todisplay satisfactory exon skipping efficiency, its length and some othercharacteristics make it less preferred from the perspective ofdeveloping such a molecule for human therapeutic use. Besides, itappears that this oligonucleotide produces intermediate bands that areneither representative of wild-type, nor of exon 73-free mRNAs. Althoughit is not known whether these bands have clinical relevance, producingby-products is less preferred from a regulatory and safety standpoint.Hence, there remains a need for further and improved therapies to treatDEB.

Thus the invention provides an antisense oligonucleotide capable ofpreventing or reducing exon 73 inclusion into the human COL7A1 mRNA,when said mRNA is produced by splicing from a pre-mRNA in a mammaliancell; characterized in that (a) the oligonucleotide's sequence includesat most two CpG sequences and/or (b) the oligonucleotide has a length ofno more than 24 nucleotides. Advantageously, the oligonucleotide hasboth properties (a) and (b).

The invention also provides an antisense oligonucleotide capable ofpreventing or reducing exon 73 inclusion into the human COL7A1 mRNA,when said mRNA is produced by splicing from a pre-mRNA in a mammaliancell, characterized in that the oligonucleotide is capable of annealingto the (SRp40/SC35 binding/ESE) element in exon 73 characterized by thesequence 5′-UUUCCUGG-3′ (SEQ ID NO: 4). This oligonucleotide can haveproperties (a) and/or (b) as discussed above.

Oligonucleotides of the invention can usefully be oligoribonucleotideswith modified internucleosidic linkages e.g. phosphorothioate linkages.They can also have modified sugars e.g. with 2′-O-methyl substitutedsugar moieties. These and other details of the oligonucleotides arediscussed below.

DESCRIPTION OF THE FIGURES

FIG. 1 shows a nucleotide sequence (SEQ ID NO: 53) which includes thehuman Col7A1 exon 73 (SEQ ID NO: 1; upper case) with its 5′ and 3′flanking intron boundaries (SEQ ID NOs: 2 & 3; lower case)

FIG. 2 shows a nucleotide sequence (SEQ ID NO: 54) which includes thelocation of SR protein binding sites in exon 73 and the location ofAONs.

FIG. 3 shows lab-on-a-chip results for exon skipping on primary humanfibroblasts (HPF) cells. The full-length mRNA gives a band at ˜350 bp,whereas mRNA with excluded exon 73 is ˜150 bp.

FIG. 4 shows the histological results of delivery of mh-AON1 formulatedin PBS using an ex vivo porcine skin model. A-B shows the results ofhaving 25 μg of mh-AON on intact skin for 24 hours, C—F shows theresults of having 25 μg of mh-AON1 on blister-like skin, with thecomplete epidermis removed. C-D: incubation for 24 hours. E-F:incubation for 48 hours. mh-AON1 is stained (red). Scale bar is 100 μm.

FIG. 5 shows the histological results of delivery of mh-AON1 formulatedinto three different hydrogels using the same ex vivo porcine skin modelas for FIG. 4. A-B shows the results of porcine skin treated with salinecontrols (A) with intact epidermis and (B) with removed epidermis. C-Dshows the porcine skin treated with 50 μg mh-AON1-cy5 mixed inFlaminal®, (C) with intact epidermis (D) with epidermis removed. E-Fshows the results with porcine skin treated with 50 μg mh-AON1-cy5 mixedin carbomer hydrogel (E) with intact epidermis and (F) with epidermisremoved. G-H shows the results with porcine skin treated with 50 μgmh-AON1-cy5 mixed in hypromellose hydrogel (G) intact skin and (H) withremoved epidermis. Scale bar indicates 100 μm. mh-AON1 is stained (red).

FIG. 6 shows lab-on-a-chip results of splicing products of COL7A1 mRNAafter treatment with mh-AON1 or the scrambled variant (SCRM) as acontrol oligo. Two different cell types we tested (HeLa and HPF), bothwith 100 nM oligonucleotide for either 24 h or 40 h. Different COL7A1mRNA products are formed after treatment with mh-AON1 or control oligo(including and excluding exon 73). The different mRNA products wereanalysed for length; 350 fragment represents the wild type, full length,mRNA and the 150 nucleotide fragment the modulated mRNA product.

FIG. 7 shows primer design for the ddPCR assay, two different primercombinations were designed to PCR either only the wild type product orthe Δ exon 73 product. Upper row: primer pair for the wild type; Lowerrow: primer pair for the skipped exon 73.

FIGS. 8A-B show the absolute quantification of COL7A1 mRNA transcriptsincluding exon 73 and excluding exon 73, in HPF cells that carry anunaltered COL7A1 sequence. A dose-response was done with mh-AON1, with50, 100 and 200 nm. FIG. 8A shows the results after 24 h. FIG. 8B showsthe results after 40 h transfection with the oligonucleotide. Black barsrepresent the full length product while the grey bars represent thetranscript Δ73.

FIG. 9 shows the results of the immunogenicity and immunotoxicityassessment of mh-AON1 in human PBMC. (a) Heat map depicting thesignificance levels of cytokine concentrations in culture supernatantafter 24 h stimulation of human PBMC with mh-AON1 (10 nM, 100 nM or 1μM) or the positive controls Poly(I:C) (1 μg/ml), CpG (10 μg/ml), LPS(100 ng/ml) and R848 (1 μM) compared to saline-treated human PBMC. Everysquare shows the reached significance level per treatment condition(geometric mean of the five human donor with triplicate measurementseach) for each measured cytokine. (b) Fold change of IFN-α2concentration in culture supernatant after 24 hrs stimulation of PBMCwith mh-AON1 or the positive controls compared to saline-treated PBMC.Bars depict the mean with SEM of triplicate measurements per human donor(in different grey tones). The dotted line at 1 depicts the relativecytokine concentration of the saline treated PMBCs. P-values in (a) and(b) were determined using the Friedman test with Dunn's post-hoc test(c) Relative number of viable PBMC expressed as fold change of Resorufinfluorescence compared to saline treated PBMC after 24 h exposure tomh-AON1 or the positive controls. Viable cell assessment was performedusing the CellTiter-Blue kit. For all individual biological replicates,fold changes were calculated by normalizing measured RFU againstgeometric mean of corresponding triplicate saline control. Results areshown per individual donor as the mean+SEM of the triplicate foldchange, normalized against the mean of its corresponding saline control(dotted line). Repeated measures One-way ANOVA with Dunnett test formultiple corrections (compared to saline) was performed. (*P<0.05,**P≤0.01, ****P<0.001).

FIG. 10 shows the results of the immunogenicity and immunotoxicityassessment of mh-AON1 and AON73.24.5 in human Ramos-Blue cells. (a)NF-kB/AP-1 activation in Ramos-Blue cells after 24 h incubation withmh-AON1 or AON73.24.5 (at several concentrations) and the TLR agonistsPoly(I:C) (1 μg/ml), CpG (10 μg/ml), LPS (100 ng/ml) and R848 (1 μM).(b) Relative number of viable Ramos-Blue cells expressed as fold changeof resorufin fluorescence compared to saline treated Ramos-Blue cellsafter 24 hrs exposure to mh-AON1, AON73.45.5 or the positive controls.Viable cell assessment was performed using the CellTiter-Blue kit. Forall individual biological replicates, fold changes were calculated bynormalizing measured O.D (in a) or RFU (in b) against geometric mean ofcorresponding triplicate saline control. Results are shown per as themean+SEM of the triplicate fold change, normalized against the mean ofits corresponding saline control (dotted line). Repeated measuresOne-way ANOVA with Dunnett test for multiple corrections (compared tosaline) was performed on the fold change values. (****P<0.0001).

DETAILED DESCRIPTION OF THE INVENTION

Surprisingly, it has now been found by the inventors of the presentinvention that antisense oligonucleotides can be designed that fulfillthe requirements for an AON to develop them into therapeutics to treathuman disease, in particular dystrophic epidermolysis bullosa (DEB).

Although AON 73.3 disclosed in WO2013/053819 appears to be satisfactoryin terms of reducing exon 73 inclusion in the COL7A1 mRNA, thisoligonucleotide is unnecessarily long with its length of 30 nt, which isless preferred from a manufacturability, CMC and cost of goods point ofview. Moreover, the INSERM oligonucleotides contain multiple CpGrepeats, which is less preferred from an immunogenicity standpoint. Itis known that CpGs, especially repeats thereof, interact with the TLR9receptor, thereby causing an immune response in the treated individualwhich may harm performance and/or cause harm to the tissues treated withthe oligonucleotide.

Preferred AONs of the invention are less than 25, preferably less than24, nucleotides in length, capable of preventing, or at least reducing,inclusion of exon 73 into the COL7A1 mRNA with high efficiency and,compared to the prior art, have fewer (and preferably no) structures orsequences that might hamper functionality.

The shortened mRNA, lacking the entire exon 73 as a result of treatmentusing AONs of the invention, will be translated into a shorter butfunctional COL VII protein.

The AONs of the invention preferably contain no more than two(preferably only one, or even none) CpG sequence(s) and/or range inlength between 16 and 24 nucleotides, while achieving exon skippingefficiencies of more than 60% (e.g. more than 70%, ideally more than 75%or 80%, preferably more than 85%, and still more preferably more than90%) as measured in HeLa cells.

In a different aspect of the invention, AONs have been designed capableof annealing to an 8-mer motif that was, until now, not recognized asbeing important in selection of the 5′ splice acceptor site flankingexon 73. It is postulated that this 8-mer motif is a previouslyoverlooked exonic splicing enhancer (ESE), that may be targeted toprevent, or at least reduce, exon 73 inclusion into the COL7A1 mRNA. Theinventors of the present invention used a microwalk technique todetermine the location of this newly recognized putative ESE, using AONscapable of annealing to the entire motif or part of the motif, designingdifferent AONs that are progressively truncated to shorten the overlapwith this motif until exon skipping is lost entirely. By so doing, theinventors identified a 5′-UUUCCUGG-3′ motif (SEQ ID NO: 4) in the5′-region of exon 73 (see FIG. 1) that forms an excellent new target forAONs to bring about prevention, or at least reduction, of exon 73inclusion into the COL7A1 mRNA.

In a further embodiment of the invention, an AON is disclosed which iscapable of efficiently preventing, or at least reducing, exon 73inclusion in the COL7A1 mRNA in both mice and humans. This AON (m-hAON1) is fully complementary to the pre-mRNA target in both mice andhumans. This AON has as advantage that it can be used to perform proofof concept studies and toxicology studies in mice using the exact samemolecule as the one that will eventually be developed for therapeuticuse in humans.

None of the AONs according to the invention appear to produceintermediate bands; only bands corresponding to the wt mRNA or bandscorresponding to a full exon 73 less mRNA appear to be generated incells treated with AONs according to the invention.

A further preferred property of AONs according to the invention is thatthey do not contain G-tetrads or multiple G's (3 or more consecutiveguanosines), thereby avoiding problems associated with multiplexformation and/or solubility.

Table 1 shows for each AON the skipping efficiency of exon 73 in HeLacells, the nucleotide sequence and SEQ ID NO of preferred AONs accordingto the invention (AON1-AON25 and m-hAON1), of the AONs used in themicro-walk to identify the new ESE-motif (AON26-30), and of truncatedversions of the AONs found to bind this ESE-motif which lack undesirablestructures such as G-tetrads (AON24.1 to 24.5) while still displayingsatisfactory exon skipping efficiencies. Further details about the AONs,their efficacy in other cells, and comparison to prior art AONs, aregiven in Example 1.

TABLE 1 Efficiency of exon 73 exclusion from mRNA. HPFand HeLa cells were treated for 24 hours with 100 nm AON. SEQ ID HeLaAON sequence 5′-3′ NO AON1  86% UCUCCAGGAAAGCCGAUGGGGCCC  5 AON2  85%AGCCCGCGUUCUCCAGGAAAGCCGA  6 AON3  92% GUCGCCCUUCAGCCCGCGUUCUCCA  7 AON4 83% ACGGUCGCCCUUCAGCCCGCGUU  8 AON5   3% CCCCUGAGGGCCAGGGUCUCCACGG  9AON6   0% CAGACCAGGUGGCCCCUGAGGGCCA 10 AON7   0%CCAAGGGCCAGACCAGGUGGCCCC 11 AON8   0% CCAGACCAGGUGGCCCCUGAGGGCC 12 AON9  0% UCUCCCCAAGGGCCAGACCAGG 13 AON10   0% GGAAGGCCCGGGGGGGCCCCUCUC 14AON11   6% CCGGCAAGGCCGGAAGGCCCGGGG 15 AON12   0%AGGCUUUCCAGGCUCCCCGGCAAG 16 AON13   2% CGGGAAUACCAGGCUUUCCAGGCU 17 AON14 25% UGCCUGGGAGCCCGGGAAUACCA 18 AON15   8% CCCACACCCCCAGCCCUGCCUGGG 19AON16   0% CCUCUCCCACACCCCCAGCCCU 20 AON17   9% UCUCUCCUGGCCUUCCUGCCUCU21 AON18  13% CACCCUCUCUCCUGGCCUUCCU 22 AON19   7%CCAGCCUCACCCUCUCUCCUGG 23 AON20 100% CUCCAGGAAAGCCGAUGGGGCCC 24 AON21 89% UCCAGGAAAGCCGAUGGGGCCC 25 AON22  85% CCAGGAAAGCCGAUGGGGCCC 26 AON23 83% CUCCAGGAAAUCCGAUGGGGCCcu 27 AON24  93% UCCAGGAAAGCCGAUGGGGCCcug 28AON24.1  73% UCCAGGAAAGCCGAUGGG 39 AON24.2  88% UCCAGGAAAGCCGAUGG 40AON24.3  79% UCCAGGAAAGCCGAUG 41 AON24.4  86% CUCCAGGAAAGCCGAUGG 42AON24.5  89% UCUCCAGGAAAGCCGAUG 43 AON25  92% CCAGGAAAGCCGAUGGGGCCcugc29 AON26  49% AGGAAAGCCGAUGGGGCCcugcag 30 AON27  37%GAAAGCCGAUGGGGCCcugcagga 31 AON28  47% AAGCCGAUGGGGCCcugcaggagu 32 AON29  0% GCCGAUGGGGCCcugcaggagugg 33 AON30   7% GAUGGGGCCcugcaggaguggaa 34mh-AON 1  91% CGUUCUCCAGGAAAGCCGAUG 35

According to one embodiment, an antisense oligonucleotide is providedthat is capable of preventing or reducing exon 73 inclusion into themammalian (preferably human) COL7A1 mRNA, when said mRNA is produced bysplicing from a pre-mRNA in a mammalian cell characterized in that theoligonucleotide's sequence has at least one of properties (a) and/or(b): (a) it includes at most two CpG sequences; and/or (b) it has alength of no more than 24 nucleotides. For property (a), theoligonucleotide preferably includes no more than one CpG sequence, andmay include only one.

According to another embodiment, an antisense oligonucleotide isprovided that is capable of preventing or reducing exon 73 inclusioninto the mammalian (preferably human) COL7A1 mRNA, when said mRNA isproduced by splicing from a pre-mRNA in a mammalian cell, characterizedin that the oligonucleotide is capable of annealing to the sequencemotif 5′-UUUCCUGG-3′ (SEQ ID NO: 4) in the 5′ upstream part of exon 73(FIG. 1). Without wishing to be bound by theory, this motif ispostulated to represent a SRp40/SC35 binding exonic splicing enhancer(ESE) element. The AONs according to this embodiment are preferablycharacterized in that the oligonucleotide's sequence has one or both ofproperties (a) and/or (b) as discussed above. In order to have optimaleffect the oligonucleotide should anneal to the entire 8-mer motif; ifexon skipping efficiencies below 60% would be acceptable for anyparticular scenario then annealing to the 6 or 7 most 5′ nucleotides ofthe 8-mer motif can be acceptable.

Further preferred AONs according to the invention are those whereinfeature (a) is characterized by that the oligonucleotide includes nomore than one CpG, and/or feature (b) is characterized in that theoligonucleotide has a length of no more than 24 nucleotides, preferablybetween 12 and 24 nucleotides, more preferably between 16 and 24nucleotides, such as 16, 17, 18, 19, 20, 21, 22, 23 or 24 nucleotidesstill more preferably less than 23 nucleotides, still more preferablybetween 16 and 23 nucleotides, such as 16, 17, 18, 19, 20, 21, 22, 23nucleotides. According to most preferred embodiments of the invention,the oligonucleotides are characterized in that they have both properties(a) at most two CpG sequences, preferably no more than one, such as oneCpG and (b) a length of no more than 24 nucleotides, preferably between12 and 24 nucleotides, more preferably between 16 and 24 nucleotides,such as 16, 17, 18, 19, 20, 21, 22, 23 or 24 nucleotides, still morepreferably less than 23 nucleotides, still more preferably between 16and 23 nucleotides, such as 16, 17, 18, 19, 20, 21, 22, 23 nucleotides.

An optional further feature of AONs according to the invention is thattheir sequence lacks a stretch of 3 or more consecutive guanosines.

Specific preferred AONs of the invention have the nucleotide sequencesAON1, AON2, AON3, AON4, AON20, AON21, AON22, AON23, AON24, AON24.1,AON24.2, AON24.3, AON24.3, AON.24.4, AON.24.5, AON25 and mh-AON1 asdisclosed in Table 1 above. More preferably for these oligo's, allribose moieties are 2′-O-methylated and substantially allinternucleosidic linkages are phosphorothioates.

In all embodiments of the present invention, the terms “preventing, orat least reducing, exon inclusion” and “exon skipping” are synonymous.In respect of COL7A1, “preventing, or at least reducing, exon inclusion”or “exon skipping” are to be construed as the exclusion of exon 73 (SEQID NO: 1, or allelic forms thereof) from the human COL7A1 mRNA (see FIG.1). The term exon skipping is herein defined as the induction within acell of a mature mRNA that does not contain a particular exon that wouldbe present in the mature mRNA without exon skipping. Exon skipping isachieved by providing a cell expressing the pre-mRNA of said mature mRNAwith a molecule capable of interfering with sequences such as, forexample, the splice donor or splice acceptor sequence required forallowing the biochemical process of splicing, or with a molecule that iscapable of interfering with an exon inclusion signal required forrecognition of a stretch of nucleotides as an exon to be included in themature mRNA; such molecules are herein referred to as exon skippingmolecules.

The term pre-mRNA refers to a non-processed or partly-processedprecursor mRNA that is synthesized from a DNA template in a cell bytranscription.

The term “antisense oligonucleotide” is understood to refer to anucleotide sequence which is complementary to a target nucleotidesequence in a pre-mRNA molecule, hnRNA (heterogeneous nuclear RNA) ormRNA molecule, so that it is capable of annealing with its correspondingtarget sequence.

The term “complementary” as used herein includes “fully complementary”and “substantially complementary”, meaning there will usually be adegree of complementarity between the oligonucleotide and itscorresponding target sequence of more than 80%, preferably more than85%, still more preferably more than 90%, most preferably more than 95%.For example, for an oligonucleotide of 20 nucleotides in length with onemismatch between its sequence and its target sequence, the degree ofcomplementarity is 95%.

The degree of complementarity of the antisense sequence is preferablysuch that a molecule comprising the antisense sequence can anneal to thetarget nucleotide sequence in the RNA molecule under physiologicalconditions, thereby facilitating exon skipping. It is well known to aperson having ordinary skill in the art, that certain mismatches aremore permissible than others, because certain mismatches have lesseffect on the strength of binding, as expressed in terms of meltingtemperature or Tm, between AON and target sequence, than others. Certainnon-complementary base pairs may form so-called “wobbles” that disruptthe overall binding to a lesser extent than true mismatches. The lengthof the AON also plays a role in the strength of binding, longer AONshaving higher melting temperatures as a rule than shorter AONs, and theG/C content of an oligonucleotide is also a factor that determines thestrength of binding, the higher the G/C content the higher the meltingtemperature for any given length. Certain chemical modifications of thenucleobases or the sugar-phosphate backbone, as contemplated by thepresent invention, may also influence the strength of binding, such thatthe degree of complementarity is only one factor to be taken intoaccount when designing an oligonucleotide according to the invention.

The presence of a CpG or multitude (two or more) of CpGs in anoligonucleotide is usually associated with an increased immunogenicityof said oligonucleotide (Dorn & Kippenberger, 2008). This increasedimmunogenicity is undesired since it may induce damage of the tissue tobe treated, i.e. the skin (dermis and/or epidermis).

The invention allows designing an oligonucleotide with acceptable RNAbinding kinetics and/or thermodynamic properties. The RNA bindingkinetics and/or thermodynamic properties are at least in part determinedby the melting temperature of an oligonucleotide (Tm; calculated withthe oligonucleotide properties calculator (available on the world wideweb at www.unc.edu/˜cail/biotool/oligo/index.html) for single strandedRNA using the basic Tm and the nearest neighbor models), and/or the freeenergy of the AON-target exon complex (using RNA structure version 4.5).If a Tm is too high, the oligonucleotide is expected to be lessspecific. An acceptable Tm and free energy depend on the sequence of theoligonucleotide, the chemistry of the backbone (phosphodiester,phosphorothioate, phosphoramidate, peptide-nucleic acid, etc.), thenature of the sugar moiety (ribose, deoxyribose, substituted ribose,intramolecular bridge) and chemical modification of the nucleobase.Therefore, the range of Tm can vary widely. In accordance with oneaspect of the invention, new AONs are provided according to theinvention by microwalking the 5′ region of exon 73 with AONs. Thus, anovel 8 nucleotide motif (a putative ESE) has been identified that formsa suitable target to design AONs according to the invention.

The length of the oligo selected by the present inventors was between 16and 24 nucleotides, but a different length is also possible. It ispreferred to have a length that is long enough to allow for a stableinteraction with the target RNA and specificity for the target sequencebut not longer than necessary, as longer oligonucleotides are moreexpensive to manufacture and are more complex from an analytical pointof view. The 5′ region of exon 73 may be probed for efficient exonskipping molecules, by making a series of overlapping oligonucleotidesthat are tested in an in vitro assay for their efficacy of exonskipping—as exemplified in the examples. The AONs that establish asatisfactory exon skipping efficacy are then further selected on thebasis of the manufacturability, immunogenicity and other usabilitycriteria provided herein.

The opposite strategy is also possible. In accordance with thisstrategy, the oligo's are first designed based on the manufacturability,immunogenicity and other usability criteria provided by the presentinvention, and are then tested for exon skipping efficiency. Afunctional activity of said oligonucleotide is preferably to induce theskipping of exon 73 (SEQ ID NO: 1) to a certain extent and/or at leastdecreasing the production of an exon 73 containing mRNA, therebyincreasing the production of a shorter than wild-type yet functionalcollagen protein.

The exon skipping percentage or efficiency may be calculated bydetermining the concentration of wild-type band amplified, divided bythe concentration of the shortened (exon 73-free) band amplified, aftera given number of PCR cycles, times 100%, for any given primer set,provided the number of cycles is such that the amplification is still inthe exponential phase. Quantification can be performed using theBioanalyzer DNA1000 apparatus

Preferred AONs according to the invention are those showing a skippingpercentage of more than 70% in AON-treated cells compared to non-treatedcells, more preferably more than 80%, still more preferably more than90%, as measured by RT-PCR analysis.

Preferably, an AON according to the invention, which comprises asequence that is complementary to a nucleotide sequence as shown in SEQID NO: 1 is such that the complementary part is at least 80%, morepreferably at least 90%, still more preferably at least 95%, most 100%complementary to the target sequence. It is thus not absolutely requiredthat all the bases in the region of complementarity are capable ofpairing with bases in the opposing strand. For instance, when designingthe oligonucleotide one may want to incorporate for instance a residuethat does not base pair with the base on the complementary strand.Mismatches may, to some extent, be allowed, if under the circumstancesin the cell, the stretch of nucleotides is sufficiently capable ofhybridizing to the complementary part. In this context, “sufficiently”means that the AONs according to the invention are capable of inducingexon skipping of exon 73. Skipping the targeted exon may conveniently beassessed by RT-PCR. The complementary regions are preferably designedsuch that, when combined, they are specific for the exon in thepre-mRNA. Such specificity may be created with various lengths ofcomplementary regions as this depends on the actual sequences in other(pre-)mRNA molecules in the system. The risk that the oligonucleotidealso will be able to hybridize to one or more other pre-mRNA moleculesdecreases with increasing size of the oligonucleotide, while the lengthshould not be too long to create problems with manufacturability,purification and/or analytics.

It is clear that oligonucleotides comprising mismatches in the region ofcomplementarity but that retain the capacity to hybridize and/or bind tothe targeted region(s) in the pre-mRNA, can be used in the presentinvention. However, preferably at least the complementary parts do notcomprise such mismatches as these typically have a higher efficiency anda higher specificity, than oligonucleotides having such mismatches inone or more complementary regions. It is thought, that higherhybridization strengths, (i.e. increasing number of interactions withthe opposing strand) are favorable in increasing the efficiency of theprocess of interfering with the splicing machinery of the system.Preferably, the complementarity is from 90% to 100%. In general thisallows for 1 or 2 mismatch(es) in an oligonucleotide of 20 nucleotides.

An exon skipping molecule of the invention is preferably an (antisense)oligonucleotide, which is complementary to SEQ ID NO: 1.

Preferably, the length of the complementary part of the oligonucleotideis the same as the length of the oligonucleotide, meaning there are no5′ or 3′ ends of the oligo that do not form a base pair with the targetRNA. Thus a preferred length for an oligonucleotide of the invention is24 nucleotides or less e.g. 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,23 or 24 nucleotides.

Particularly good results have been obtained with AONs having a lengthbetween 16 and 24 nucleotides.

An exon skipping molecule according to the invention may contain one ofmore DNA residues (consequently a RNA “u” residue will be a “t” residueas DNA counterpart), or one or more RNA residues, and/or one or morenucleotide analogues or equivalents, as will be further detailed hereinbelow. SEQ ID NOs: 5-35 & 39-43 are RNA sequences, but the inventionalso encompasses each of these sequences in DNA form, and also DNA/RNAhybrids of these sequences.

It is preferred that an exon skipping molecule of the inventioncomprises one or more residues that are modified to increase nucleaseresistance, and/or to increase the affinity of the antisenseoligonucleotide for the target sequence. Therefore, in a preferredembodiment, the antisense nucleotide sequence comprises at least onenucleotide analogue or equivalent, wherein a nucleotide analogue orequivalent is defined as a residue having a modified base, and/or amodified backbone, and/or a non-natural internucleoside linkage, or acombination of these modifications.

In a preferred embodiment, the nucleotide analogue or equivalentcomprises a modified backbone. Examples of such backbones are providedby morpholino backbones, carbamate backbones, siloxane backbones,sulfide, sulfoxide and sulfone backbones, formacetyl and thioformacetylbackbones, methyleneformacetyl backbones, riboacetyl backbones, alkenecontaining backbones, sulfamate, sulfonate and sulfonamide backbones,methyleneimino and methylenehydrazino backbones, and amide backbones.Phosphorodiamidate morpholino oligomers are modified backboneoligonucleotides that have previously been investigated as antisenseagents. Morpholino oligonucleotides have an uncharged backbone in whichthe deoxyribose sugar of DNA is replaced by a six membered ring and thephosphodiester linkage is replaced by a phosphorodiamidate linkage.Morpholino oligonucleotides are resistant to enzymatic degradation andappear to function as antisense agents by arresting translation orinterfering with pre-mRNA splicing rather than by activating RNase H.Morpholino oligonucleotides have been successfully delivered to tissueculture cells by methods that physically disrupt the cell membrane, andone study comparing several of these methods found that scrape loadingwas the most efficient method of delivery; however, because themorpholino backbone is uncharged, cationic lipids are not effectivemediators of morpholino oligonucleotide uptake in cells.

According to one embodiment of the invention the linkage between theresidues in a backbone do not include a phosphorus atom, such as alinkage that is formed by short chain alkyl or cycloalkylinternucleoside linkages, mixed heteroatom and alkyl or cycloalkylinternucleoside linkages, or one or more short chain heteroatomic orheterocyclic internucleoside linkages.

In accordance with this embodiment, a preferred nucleotide analogue orequivalent comprises a Peptide Nucleic Acid (PNA), having a modifiedpolyamide backbone (Nielsen, et al. (1991) Science 254, 1497-1500).PNA-based molecules are true mimics of DNA molecules in terms ofbase-pair recognition. The backbone of the PNA is composed ofN-(2-aminoethyl)-glycine units linked by peptide bonds, wherein thenucleobases are linked to the backbone by methylene carbonyl bonds. Analternative backbone comprises a one-carbon extended pyrrolidine PNAmonomer (Govindaraju and Kumar (2005) Chem. Commun, 495-497). Since thebackbone of a PNA molecule contains no charged phosphate groups, PNA-RNAhybrids are usually more stable than RNA-RNA or RNA-DNA hybrids,respectively (Egholm et al. (1993) Nature 365, 566-568).

According to another embodiment of the invention, the backbone comprisesa morpholino nucleotide analog or equivalent, in which the ribose ordeoxyribose sugar is replaced by a 6-membered morpholino ring. A mostpreferred nucleotide analog or equivalent comprises a phosphorodiamidatemorpholino oligomer (PMO), in which the ribose or deoxyribose sugar isreplaced by a 6-membered morpholino ring, and the anionic phosphodiesterlinkage between adjacent morpholino rings is replaced by a non-ionicphosphorodiamidate linkage.

In yet a further embodiment, a nucleotide analogue or equivalent of theinvention comprises a substitution of one of the non-bridging oxygens inthe phosphodiester linkage. This modification slightly destabilizesbase-pairing but adds significant resistance to nuclease degradation. Apreferred nucleotide analogue or equivalent comprises phosphorothioate,chiral phosphorothioate, phosphorodithioate, phosphotriester,aminoalkylphosphotriester, H-phosphonate, methyl and other alkylphosphonate including 3′-alkylene phosphonate, 5′-alkylene phosphonateand chiral phosphonate, phosphinate, phosphoramidate including 3′-aminophosphoramidate and aminoalkylphosphoramidate, thionophosphoramidate,thionoalkylphosphonate, thionoalkylphosphotriester, selenophosphate orboranophosphate.

A further preferred nucleotide analogue or equivalent of the inventioncomprises one or more sugar moieties that are mono- or disubstituted atthe 2′, 3′ and/or 5′ position such as a —OH; —F; substituted orunsubstituted, linear or branched lower (C1-C10) alkyl, alkenyl,alkynyl, alkaryl, allyl, or aralkyl, that may be interrupted by one ormore heteroatoms; O-, S-, or N-alkyl; O-, S-, or N-alkenyl; O-, S- orN-alkynyl; O-, S-, or N-allyl; O-alkyl-O-alkyl, -methoxy, -aminopropoxy;methoxyethoxy; -dimethylaminooxyethoxy; and -dimethylaminoethoxyethoxy.The sugar moiety can be a furanose or derivative thereof, or adeoxyfuranose or derivative thereof, preferably ribose or derivativethereof, or deoxyribose or derivative of. A preferred derivatized sugarmoiety comprises a Locked Nucleic Acid (LNA), in which the 2′-carbonatom is linked to the 3′ or 4′ carbon atom of the sugar ring therebyforming a bicyclic sugar moiety. A preferred LNA comprises2′-0,4′-C-ethylene-bridged nucleic acid (Morita et al. 2001. NucleicAcid Res Supplement No. 1: 241-242). These substitutions render thenucleotide analogue or equivalent RNase H and nuclease resistant andincrease the affinity for the target RNA.

It is understood by a skilled person that it is not necessary for allinternucleosidic linkages in an antisense oligonucleotide to bemodified. For example, some internucleosidic linkages may be unmodified,whereas other internucleosidic linkages are modified. AONs comprising abackbone consisting of one form of (modified) internucleosidic linkages,multiple forms of (modified) internucleosidic linkages, uniformly ornon-uniformly distributed along the length of the AON are allencompassed by the present invention. In addition, any modality ofbackbone modification (uniform, non-uniform, mono-form or pluriform andall permutations thereof) may be combined with any form or of sugar ornucleoside modifications or analogues mentioned below.

An especially preferred backbone for the AONs according to the inventionis a uniform (all) phosphorothioate (PS) backbone.

In another embodiment, a nucleotide analogue or equivalent of theinvention comprises one or more base modifications or substitutions.Modified bases comprise synthetic and natural bases such as inosine,xanthine, hypoxanthine and other -aza, deaza, -hydroxy, -halo, -thio,thiol, -alkyl, -alkenyl, -alkynyl, thioalkyl derivatives of pyrimidineand purine bases that are or will be known in the art.

It is understood by a skilled person that it is not necessary for allpositions in an antisense oligonucleotide to be modified uniformly. Inaddition, more than one of the aforementioned analogues or equivalentsmay be incorporated in a single antisense oligonucleotide or even at asingle position within an antisense oligonucleotide. In certainembodiments, an antisense oligonucleotide of the invention has at leasttwo different types of analogues or equivalents.

According to another embodiment AONs according to the invention comprisea 2′-O (preferably lower) alkyl phosphorothioate antisenseoligonucleotide, such as 2′-O-methyl modified ribose (RNA),2′-O-methoxyethyl modified ribose, 2′-O-ethyl modified ribose,2′-O-propyl modified ribose, and/or substituted derivatives of thesemodifications such as halogenated derivatives.

An effective and preferred antisense oligonucleotide format according tothe invention comprises 2′-O-methyl modified ribose moieties with aphosphorothioate backbone, preferably wherein substantially all ribosemoieties are 2′-O-methyl and substantially all internucleosidic linkagesare phosphorothioate linkages.

It will also be understood by a skilled person that different antisenseoligonucleotides can be combined for efficiently skipping of exon 73 ofthe COL7A1 gene. A combination of two antisense oligonucleotides may beused in a method of the invention, such as two antisenseoligonucleotides, three different antisense oligonucleotides, fourdifferent antisense oligonucleotides, or five different antisenseoligonucleotides targeting the same or different regions of exon 73(FIG. 1), as long as at least one AON is one according to the invention.

An antisense oligonucleotide can be linked to a moiety that enhancesuptake of the antisense oligonucleotide in cells, preferably skin cells.Examples of such moieties are cholesterols, carbohydrates, vitamins,biotin, lipids, phospholipids, cell-penetrating peptides including butnot limited to antennapedia, TAT, transportan and positively chargedamino acids such as oligoarginine, poly-arginine, oligolysine orpolylysine, antigen-binding domains such as provided by an antibody, aFab fragment of an antibody, or a single chain antigen binding domainsuch as a camelid single domain antigen-binding domain.

An exon skipping molecule according to the invention may be a naked(gymnotic) antisense oligonucleotide or in the form of a conjugate orexpressed from a vector (vectored AON). The exon skipping molecule maybe administrated using suitable means known in the art. When the exonskipping molecule is a vectored AON, it may for example be provided toan individual or a cell, tissue or organ of said individual in the formof an expression vector wherein the expression vector encodes atranscript comprising said oligonucleotide. The expression vector ispreferably introduced into a cell, tissue, organ or individual via agene delivery vehicle, such as a viral vector. In a preferredembodiment, there is provided a viral-based expression vector comprisingan expression cassette or a transcription cassette that drivesexpression or transcription of an exon skipping molecule as identifiedherein. Accordingly, the present invention provides a viral vectorexpressing an exon skipping molecule according to the invention whenplaced under conditions conducive to expression of the exon skippingmolecule. A cell can be provided with an exon skipping molecule capableof interfering with sequences essential for, or at least conducive to,exon 73 inclusion, such that such interference prevents, or at leastreduces, exon 73 inclusion into the COL7A1 mRNA, for example byplasmid-derived antisense oligonucleotide expression or viral expressionprovided by adenovirus- or adeno-associated virus-based vectors.Expression may be driven by a polymerase III promoter, such as a U1, aU6, or a U7 RNA promoter. A preferred delivery vehicle is a viral vectorsuch as an adeno-associated virus vector (AAV), or a retroviral vectorsuch as a lentivirus vector and the like. Also, plasmids, artificialchromosomes, plasmids usable for targeted homologous recombination andintegration in the mammalian (preferably human) genome of cells may besuitably applied for delivery of an oligonucleotide as defined herein.Preferred for the current invention are those vectors whereintranscription is driven from PolIII promoters, and/or whereintranscripts are in the form of fusions with U1 or U7 transcripts, whichyield good results for delivering small transcripts. It is within theskill of the artisan to design suitable transcripts. Preferred arePolIII driven transcripts. Preferably, in the form of a fusiontranscript with an U1 or U7 transcript. Such fusions may be generated asdescribed in the art (e.g. vide: Gorman L et al., 1998 or Suter D etal., 1999).

One preferred antisense oligonucleotide expression system is anadenovirus associated virus (AAV)-based vector. Single chain and doublechain AAV-based vectors have been developed that can be used forprolonged expression of antisense nucleotide sequences for highlyefficient skipping of COL7A1 exon 73.

A preferred AAV-based vector for instance comprises an expressioncassette that is driven by a polymerase III-promoter (Pol III). Apreferred Pol III promoter is, for example, a U1, a U6, or a U7 RNApromoter.

The invention therefore also provides a viral-based vector, comprising aPol III-promoter driven expression cassette for expression of anantisense oligonucleotide of the invention for inducing skipping ofCOL7A1 exon 73.

An AAV vector according to the present invention is a recombinant AAVvector and refers to an AAV vector comprising part of an AAV genomecomprising an encoded exon skipping molecule according to the inventionencapsidated in a protein shell of capsid protein derived from an AAVserotype as depicted elsewhere herein. Part of an AAV genome may containthe inverted terminal repeats (ITR) derived from an adeno-associatedvirus serotype, such as AAV1, AAV2, AAV3, AAV4, AAV5, AAV8, AAV9 andothers. Protein shell comprised of capsid protein may be derived from anAAV serotype such as AAV1, 2, 3, 4, 5, 8, 9 and others. A protein shellmay also be named a capsid protein shell. AAV vector may have one orpreferably all wild type AAV genes deleted, but may still comprisefunctional ITR nucleic acid sequences. Functional ITR sequences arenecessary for the replication, rescue and packaging of AAV virions. TheITR sequences may be wild type sequences or may have at least 80%, 85%,90%, 95, or 100% sequence identity with wild type sequences or may bealtered by for example in insertion, mutation, deletion or substitutionof nucleotides, as long as they remain functional. In this context,functionality refers to the ability to direct packaging of the genomeinto the capsid shell and then allow for expression in the host cell tobe infected or target cell. In the context of the present invention acapsid protein shell may be of a different serotype than the AAV vectorgenome ITR. An AAV vector according to present the invention may thus becomposed of a capsid protein shell, i.e. the icosahedral capsid, whichcomprises capsid proteins (VP1, VP2, and/or VP3) of one AAV serotype,e.g. AAV serotype 2, whereas the ITRs sequences contained in that AAV5vector may be any of the AAV serotypes described above, including anAAV2 vector. An “AAV2 vector” thus comprises a capsid protein shell ofAAV serotype 2, while e.g. an “AAV5 vector” comprises a capsid proteinshell of AAV serotype 5, whereby either may encapsidate any AAV vectorgenome ITR according to the invention.

Preferably, a recombinant AAV vector according to the present inventioncomprises a capsid protein shell of AAV serotype 2, 5, 8 or AAV serotype9 wherein the AAV genome or ITRs present in said AAV vector are derivedfrom AAV serotype 2, 5, 8 or AAV serotype 9; such AAV vector is referredto as an AAV2/2, AAV 2/5, AAV2/8, AAV2/9, AAV5/2, AAV5/5, AAV5/8, AAV5/9, AAV8/2, AAV 8/5, AAV8/8, AAV8/9, AAV9/2, AAV9/5, AAV9/8, or anAAV9/9 vector, respectively.

More preferably, a recombinant AAV vector according to the presentinvention has tropism for dermal and epidermal cells and comprises acapsid protein shell of AAV serotype 5 or 8. The AAV genome or ITRspresent in said vector may be derived from the same or a differentserotype, such as AAV serotype 2; such vector is referred to as an AAV2/5 or AAV 2/8 vector. AAV with a serotype 5 capsid have tropism fordermal and epidermal cells, such as basilar and suprabasilarkeratinocytes and dermal fibroblasts. AAV vectors with a type 5 capsiddisplay much higher transduction efficiencies compared to AAV with atype 2 capsid (Keswani et al. Wound Repair Regen. 2012; 20(4): 592-600).Similarly, AAV with a capsid of serotype 8 show tropism towards dermalfibroblasts and (mainly) suprabasilar keratinocytes. Moreover, AAV 2/8tend to be more efficient in transducing mammalian, preferably humandermal and epidermal cells than AAV 2/5. However, transductionefficiency appears to depend on the timing of administration duringwound healing, AAV 2/2 showing higher transduction efficiencies than AAV2/5 and AAV 2/8 at later time points (Keswani et al., supra).

Hence, AAV 2/2, AAV x/5 and AAV x/8 are preferred AAV to deliver AONsaccording to the invention and their choice may be determined takinginto account the time of administration and the cell types to betargeted. These details can be readily worked out a person skilled inthe art, in pre-clinical or clinical studies.

A nucleic acid molecule encoding an exon skipping molecule according tothe present invention represented by a nucleic acid sequence of choiceis preferably inserted between the AAV genome or ITR sequences asidentified above, for example an expression construct comprising anexpression regulatory element operably linked to a coding sequence and a3′ termination sequence.

“AAV helper functions” generally refers to the corresponding AAVfunctions required for AAV replication and packaging supplied to the AAVvector in trans. AAV helper functions complement the AAV functions whichare missing in the AAV vector, but they lack AAV ITRs (which areprovided by the AAV vector genome). AAV helper functions include the twomajor ORFS of AAV, namely the rep coding region and the cap codingregion or functional substantially identical sequences thereof. Rep andCap regions are well known in the art, see e.g. Chiorini et al. (1999,J. of Virology, Vol 73(2): 1309-1319) or U.S. Pat. No. 5,139,941,incorporated herein by reference. The AAV helper functions can besupplied on a AAV helper construct, which may be a plasmid. Introductionof the helper construct into the host cell can occur e.g. bytransformation, transfection, or transduction prior to or concurrentlywith the introduction of the AAV genome present in the AAV vector asidentified herein. The AAV helper constructs of the invention may thusbe chosen such that they produce the desired combination of serotypesfor the AAV vector's capsid protein shell on the one hand and for theAAV genome present in said AAV vector replication and packaging on theother hand.

“AAV helper virus” provides additional functions required for AAVreplication and packaging. Suitable AAV helper viruses includeadenoviruses, herpes simplex viruses (such as HSV types 1 and 2) andvaccinia viruses. The additional functions provided by the helper viruscan also be introduced into the host cell via vectors, as described inU.S. Pat. No. 6,531,456 incorporated herein by reference.

Preferably, an AAV genome as present in a recombinant AAV vectoraccording to the present invention does not comprise any nucleotidesequences encoding viral proteins, such as the rep (replication) or cap(capsid) genes of AAV. An AAV genome may further comprise a marker orreporter gene, such as a gene for example encoding an antibioticresistance gene, a fluorescent protein (e.g. gfp) or a gene encoding achemically, enzymatically or otherwise detectable and/or selectableproduct (e.g. lacZ, aph, etc.) known in the art.

A preferred AAV vector according to the present invention is an AAVvector, preferably an AAV2/5, AAV2/8, AAV2/9 or AAV2/2 vector,expressing an exon skipping molecule according to the present inventioncomprising an antisense oligonucleotide, wherein said antisenseoligonucleotide comprises or consists of a sequence selected from thegroup consisting of: AON1, AON2, AON3, AON4, AON20, AON21, AON22, AON23,AON24, AON24.1, AON24.2, AON24.3, AON24.3, AON.24.4, AON.24.5, AON25 andmh-AON1 as disclosed in Table 1 above.

Improvements in means for providing an individual or a cell, tissue,organ of said individual with an exon skipping molecule according to theinvention, are anticipated considering the progress that has alreadythus far been achieved. Such future improvements may of course beincorporated to achieve the mentioned effect on restructuring of mRNAusing a method of the invention. An exon skipping molecule according tothe invention can be delivered as is to an individual, a cell, tissue ororgan of said individual. When administering an exon skipping moleculeaccording to the invention, it is preferred that the molecule isdissolved in a solution that is compatible with the delivery method.

Gymnotic AONs are readily taken up by most cells in vivo, and usuallydissolving the AONs according to the invention in an isotonic (saline)solution will be sufficient to reach the target cells, such as skin(dermis and epidermis) cells. Alternatively, gymnotic AONs of theinvention may be formulated using pharmaceutically acceptableexcipients, additives, stabilizers, solvents, colorants and the like. Inaddition, or alternatively, gymnotic AONs may be formulated with any ofthe transfection aids mentioned below.

Skin (dermis and epidermis) cells can be provided with a plasmid forantisense oligonucleotide expression by providing the plasmid in anaqueous solution, such as an isotonic (saline) solution. Alternatively,a plasmid can be provided by transfection using known transfectionagents.

For intravenous, subcutaneous, intramuscular, intrathecal and/orintradermal administration it is preferred that the solution is anisotonic (saline) solution. Particularly preferred in the invention isthe use of an excipient or transfection agents that will aid in deliveryof each of the constituents as defined herein to a cell and/or into acell, preferably a skin (dermis and epidermis) cell. Preferred areexcipients or transfection agents capable of forming complexes,nanoparticles, micelles, vesicles and/or liposomes that deliver eachconstituent as defined herein, complexed or trapped in a vesicle orliposome through a cell membrane. Many of these excipients are known inthe art. Suitable excipients or transfection agents comprisepolyethylenimine (PEI; ExGen500 (MBI Fermentas)), LipofectAMINE™ 2000(Invitrogen) or derivatives thereof, or similar cationic polymers,including polypropyleneimine or polyethylenimine copolymers (PECs) andderivatives, synthetic amphiphils (SAINT-18), Iipofectin™, DOTAP and/orviral capsid proteins that are capable of self-assembly into particlesthat can deliver each constituent as defined herein to a cell,preferably a skin (dermis or epidermis) cell. Such excipients have beenshown to efficiently deliver an oligonucleotide such as antisensenucleic acids to a wide variety of cultured cells, including skin(dermis and epidermis) cells. Their high transfection potential iscombined with an acceptably low to moderate toxicity in terms of overallcell survival. The ease of structural modification can be used to allowfurther modifications and the analysis of their further (in vivo)nucleic acid transfer characteristics and toxicity.

Lipofectin represents an example of a liposomal transfection agent. Itconsists of two lipid components, a cationic lipid N-[1-(2,3dioleoyloxy)propyl]-N,N,N-trimethylammonium chloride (DOTMA) (cp. DOTAPwhich is the methylsulfate salt) and a neutral lipiddioleoylphosphatidylethanolamine (DOPE). The neutral component mediatesthe intracellular release. Another group of delivery systems arepolymeric nanoparticles.

Polycations such like diethylaminoethylaminoethyl (DEAE)-dextran, whichare well known as DNA transfection reagent can be combined withbutylcyanoacrylate (PBCA) and hexylcyanoacrylate (PHCA) to formulatecationic nanoparticles that can deliver each constituent as definedherein, preferably an oligonucleotide, across cell membranes into cells.

In addition to these common nanoparticle materials, the cationic peptideprotamine offers an alternative approach to formulate an oligonucleotidewith colloids. This colloidal nanoparticle system can form so calledproticles, which can be prepared by a simple self-assembly process topackage and mediate intracellular release of an oligonucleotide. Theskilled person may select and adapt any of the above or othercommercially available alternative excipients and delivery systems topackage and deliver an exon skipping molecule for use in the currentinvention to deliver it for the prevention, treatment or delay of adisease or condition associated with a mutated exon 73 in the COL7A1gene.

An exon skipping molecule according to the invention could be covalentlyor non-covalently linked to a targeting ligand specifically designed tofacilitate the uptake into the cell (especially a skin (dermis) cell),cytoplasm and/or its nucleus. Such ligand could comprise (i) a compound(including but not limited to peptide(-like) structures) recognizingcell, tissue or organ specific elements facilitating cellular uptakeand/or (ii) a chemical compound able to facilitate the uptake in tocells and/or the intracellular release of an oligonucleotide fromvesicles, e.g. endosomes or lysosomes.

Therefore, in a preferred embodiment, an exon skipping moleculeaccording to the invention is formulated in a composition or amedicament or a composition, which is provided with at least anexcipient and/or a targeting ligand for delivery and/or a deliverydevice thereof to a cell and/or enhancing its intracellular delivery.

Preferred delivery is through topical administration. As outlined in theaccompanying examples such may be through the use of a pharmaceuticallyacceptable hydrogel, such as Flaminal Hydro®, which is a hydrogelalready used in patient care, (2) a hypromellose hydrogel or (3) acarbomer hydrogel. Topical formulations that may be used for the topicaldelivery of the oligonucleotides of the present invention are:

-   -   Creams, either formulated as a water-in-oil or as an        oil-in-water emulsion; the latter are more cosmetically and        aesthetically acceptable. Examples are Softisan based creams or        cetomacrogol creams.    -   Gels: Solutions or suspensions, which contain a gelling agent        that is uniformly distributed throughout the liquid phase.        Examples are hydrogels including, but not limited to        hypromellose, carbomer and alginate.    -   Ointments. These usually contain <20% water and >50%        hydrocarbons, waxes or polyols as the vehicle. They have a more        greasy skin feel than creams.    -   Pastes: These contain a high percentage of finely dispersed        solids with a stiff consistency.    -   Suspensions, which are liquid preparations that contain solid        particles dispensed in a liquid vehicle. Some can be labeled as        lotions.    -   Lotions. These are fluid, somewhat viscous (emulsion)        formulations, which share many characteristics with suspensions,        low viscosity gels and solutions.    -   Foams, which are emulsions that have a fluffy consistency, when        dispensed.    -   Sprays, which are fine, small droplets of liquid, generated by a        nozzle.    -   Solutions, which are liquid products that are usually aqueous,        but may contain other solvents such as alcohols.

It is to be understood that if a composition comprises an additionalconstituent such as an adjunct compound defined herein, each constituentof the composition may be formulated in one single combination orcomposition or preparation. Depending on their identity, the skilledperson will know which type of formulation is the most appropriate foreach constituent as defined herein. According to one embodiment, theinvention provides a composition or a preparation which is in the formof a kit of parts comprising an exon skipping molecule according to theinvention and a further adjunct compound as defined herein.

If required, an exon skipping molecule according to the invention or avector, preferably a viral vector, expressing an exon skipping moleculeaccording to the invention can be incorporated into a pharmaceuticallyactive mixture by adding a pharmaceutically acceptable carrier.

Accordingly, the invention also provides a composition, preferably apharmaceutical composition, comprising an exon skipping moleculeaccording to the invention, such as gymnotic AON or a viral vectoraccording to the invention and a pharmaceutically acceptable excipient.Such composition may comprise a single exon skipping molecule accordingto the invention, but may also comprise multiple, distinct exon skippingmolecules according to the invention. Such a pharmaceutical compositionmay comprise any pharmaceutically acceptable excipient, including acarrier, filler, preservative, adjuvant, solubilizer and/or diluent.Such pharmaceutically acceptable carrier, filler, preservative,adjuvant, solubilizer and/or diluent may for instance be found inRemington, 2000. Each feature of said composition has earlier beendefined herein.

If multiple distinct exon skipping molecules according to the inventionare used, concentration or dose defined herein may refer to the totalconcentration or dose of all oligonucleotides used or the concentrationor dose of each exon skipping molecule used or added. Therefore in oneembodiment, there is provided a composition wherein each or the totalamount of exon skipping molecules according to the invention used isdosed in an amount ranged from 0.0001 and 100 mg/kg, preferably from0.001 and 50 mg/kg, still more preferably between 0.01 and 20 mg/kg.

A preferred exon skipping molecule according to the invention, is forthe treatment of DEB, or, more generally, a mutated COL7A1 exon 73related disease or condition of an individual. In all embodiments of thepresent invention, the term “treatment” is understood to include theprevention and/or delay of the disease or condition. An individual,which may be treated using an exon skipping molecule according to theinvention may already have been diagnosed as having DEB or a COL7A1 exon73 related disease or condition. Alternatively, an individual which maybe treated using an exon skipping molecule according to the inventionmay not have yet been diagnosed, but may be an individual having anincreased risk of developing DEB, or a COL7A1 exon 73 related disease orcondition in the future given his or her genetic background. A preferredindividual is a human being. In a preferred embodiment the mutatedCOL7A1 exon 73 related disease or condition is DEB.

The present invention further provides an exon skipping moleculeaccording to the invention, such as an AON, or a vector encoding an AON,such as a viral vector, according to the invention, or a compositioncomprising an AON, or a vector encoding an AON, according to theinvention for use as a medicine e.g. for use in treating DEB or, moregenerally, a mutated COL7A1 exon 73 related disease or condition of anindividual (as discussed above).

The invention further provides the use of an exon skipping moleculeaccording to the invention, such as an AON, or a vector encoding an AON,such as a viral vector, according to the invention, or a compositioncomprising an AON, or a vector encoding an AON, according to theinvention in the manufacture of a medicament for treating DEB or, moregenerally, a mutated COL7A1 exon 73 related disease or condition of anindividual (as discussed above).

The invention further provides a method for treating a mammal(preferably a human) carrying in its genome a mutation in exon 73 of theCOL7A1 gene causing a disease or disorder, including DEB, comprisingadministering to the mammal (human) an AON, a (viral) vector, or apharmaceutical composition of the invention. These patients may suffer,or be at risk of developing DEB or a related disorder. Related disorder,disease or condition also encompasses for example skin cancer (squamouscell carcinoma), or other carcinomas, that may arise as a consequence ofa collagen VII deficiency or abnormality in the skin, or other organs ofan individual, caused by or associated with a mutation in exon 73 of theCOL7A1 gene.

Further embodiments of the invention are AONs, viral vectors encodingAONs, and pharmaceutical compositions comprising AONs according to theinvention for use as a medicine to treat a mammal (preferably a human)carrying in its genome a mutation in exon 73 of the COL7A1 gene.

Exon skipping molecules according to the invention may be administeredto a patient systemically, locally, topically, through administrationthat is orally, intraocularly, intrapulmonary, intranasally,intramuscularly, subcutaneously, intradermally, rectally, by swallowing,injecting, inhalation, infusion, spraying, in the form of (aqueous)solutions, suspensions, (oil-in-water) emulsions, ointments, lozenges,pills etcetera.

Dosing may be daily, weekly, monthly, quarterly, once per year,depending on the route of administration and the need of the patient.

Because of the early onset of disease, patients having or at risk ofdeveloping a disease, disorder or condition caused by or associated witha mutated exon 73 of the COL7A1 gene, including DEB, may be treated inutero, directly after birth, from 1, 2, 3, 6 months of age, from oneyear of age, from 3 years of age, from 5 years of age, prior to or afterthe onset of symptoms, to alleviate, retard development, stop or reversethe symptoms of disease and the like.

A treatment in a use or in a method according to the invention is atleast one week, at least one month, at least several months, at leastone year, at least 2, 3, 4, 5, 6 years or chronically, even during apatient's entire life. Each exon skipping molecule or exon skippingoligonucleotide or equivalent thereof as defined herein for useaccording to the invention may be suitable for direct administration toa cell, tissue and/or an organ in vivo of individuals already affectedor at risk of developing a mutated COL7A1 exon 73 related disorder,disease or condition, and may be administered directly in vivo, ex vivoor in vitro. The frequency of administration of an oligonucleotide,composition, compound or adjunct compound of the invention may depend onseveral parameters such as the age of the patient, the nature of theexon skipping molecule (e.g. gymnotic AON or vectored AON, such as AAVor lentiviral vector expressed AONs), the dose, the formulation of saidmolecule and the like.

Dose ranges of an exon skipping molecule, preferably an oligonucleotideaccording to the invention are preferably designed on the basis ofrising dose studies in clinical trials (in vivo use) for which rigorousprotocol requirements exist. An oligonucleotide as defined herein may beused at a dose range from 0.0001 to 100 mg/kg, preferably from 0.01 to20 mg/kg. The dose and treatment regime may vary widely, depending onmany factors, including but not limited to the route of administration(e.g. systemic versus topically), whether the oligo is administered as agymnotic AON or as vectored AON, the dosing regimen, the age and weightof the patient, and so forth.

In a preferred embodiment, a viral vector, preferably an AAV vector asdescribed earlier herein, as delivery vehicle for a molecule accordingto the invention, is administered in a dose ranging from 1×10⁹-1×10¹⁷virus particles per injection, more preferably from 1×10¹⁰-1×10¹⁴, andmost preferably 1×10¹⁰-1×10¹² virus particles per injection.

It will be clear to a person having ordinary skill in the art to whichthis invention pertains, that the details of treatment will need to beestablished in accordance with and depending on such factors as thesequence and chemistry of the oligonucleotide(s), the route ofadministration, the formulation, the dose, the dosing regimen, theformat (viral vector or gymnotic oligonucleotide), the age and weight ofthe patient, the stage of the disease and so forth, which may requirefurther non-clinical and clinical investigation.

The invention further provides a method for preventing, or at leastreducing, COL7A1 exon 73 inclusion in a cell comprising contacting thecell, preferably a skin cell (dermal fibroblast), with an exon skippingmolecule according to the invention, such as a gymnotic AON or a (viral)vector encoding an AON according to the invention, or a compositionaccording to the invention. The features of this aspect are preferablythose defined earlier herein.

Unless otherwise indicated each embodiment as described herein may becombined with another embodiment as described herein.

The ability of an exon skipping molecule, such as an AON according tothe invention, or a (viral) vector encoding such AON, to prevent, or atleast reduce, mutated COL7A1 exon 73 inclusion, when the COL7A1 gene isexpressed in a mammalian (preferably human) cell, and to bind to themammalian (human) COL7A1 pre-mRNA under physiological conditions in aregion affecting selection of the 5′ splice acceptor, and thereby reduceinclusion of the mutated exon 73 into the COL7A1 mRNA, can beconveniently assessed using the assays disclosed in the experimentalsection herein. In particular, the exon skipping molecule can beincubated with a cell containing exon 73 (not necessarily mutated) ofthe COL7A1 gene to assess its ability to reduce production by the cellof mRNA which includes exon 73, e.g. by RT-PCR (which can be quantifiedusing a Bioanalyzer apparatus), as described herein in the experimentalsection and the examples.

As can be observed in the experimental section and the Examples herein,at the RNA level, addition of various AONs according to the inventiontargeting exon 73 of the COL7A1 gene indeed resulted in a mRNA lackingexon73, leading to the production of a shorter but functional collagenVII protein.

In fibroblasts (that can be derived from the dermis part of the skin),collagen VII is abundantly expressed. Therefore, it is to be expectedthat addition of AONs to cultured fibroblasts from DEB patients willresult in an increased amount of shortened but functional collagen VIIprotein that is detectable on Western blot, and as such will demonstratethat AON-based therapy will not only redirect splicing of the COL7A1mRNA but will also result in restoring collagen VII functionality.

The terms “adenine”, “guanine”, “cytosine”, “thymine”, “uracil” andhypoxanthine (the nucleobase in inosine) refer to the nucleobases assuch.

The terms adenosine, guanosine, cytidine, thymidine, uridine andinosine, refer to the nucleobases linked to the (desoxy)ribosyl sugar.

The term “nucleoside” refers to the nucleobase linked to the(deoxy)ribosyl sugar.

In this document and in its claims, the verb “to comprise” and itsconjugations is used in its non-limiting sense to mean that itemsfollowing the word are included, but items not specifically mentionedare not excluded. In addition, reference to an element by the indefinitearticle “a” or “an” does not exclude the possibility that more than oneof the element is present, unless the context clearly requires thatthere be one and only one of the elements. The indefinite article “a” or“an” thus usually means “at least one”.

The word “include” and all of its tenses and conjugations, is to be readas “include, but is not limited to”.

The word “exon skipping molecule” is meant to include gymnotic AONs andvectored AONs, including viral vectors, capable of expressing AONs in acompatible cell.

The word “about” or “approximately” when used in association with anumerical value (e.g. about 10) preferably means that the value may bethe given value (of 10) plus or minus 5% of the value.

The sequence information as provided herein should not be so narrowlyconstrued as to require inclusion of erroneously identified bases. Theskilled person is capable of identifying such erroneously identifiedbases and knows how to correct for such errors. In case of sequenceerrors, the sequence of the polypeptide obtainable by expression of thegene present in SEQ ID NO: 1 containing the nucleic acid sequence codingfor the polypeptide should prevail.

EXAMPLES Example 1: mRNA Analysis of Exon 73

To detect the presence of mRNA of exon 73 in mRNA of COL7A1 extractedmRNA of both HeLa cells and human primary fibroblasts (HPF) were used.Culturing of cells was performed in (a) Dulbecco's Modified Eagle Medium(DMEM) supplemented with 10% fetal bovine serum (FBS) for HeLa, or (b)DMEM AQE supplemented with 20% FBS and 1% natrium pyruvate for HPFcells. All cells were grown at 37° C. 5% CO₂.

To determine the exon skip efficiency of described AONs, cells wereseeded at 60.000 cells/well (HeLa) into 12-well plates or 150.000cells/well (PHF) into 6-well plates. After 24 hours of allowing cellsgrowth cells were transfected with 100 nm AON-maxPei complex. RNAisolation was performed with the ReliaPrep™ RNA Cell Miniprep System(Promega), subsequently cDNA was made using the Thermo Scientific Versokit. PCR for exon 73 was performed with FW primer(5′-GCTGGCATCAAGGCATCT-3′; SEQ ID NO: 51) located at the exon 71-72boundary and RV primer (5′-TCCTTTCTCTCCCCGTTCTC-3′; SEQ ID NO: 52)located within exon 74. PCR products were visualized with theBioanalyzer using DNA1000 chips and software Expert 2100 was used forproduct length analysis.

Skipping efficiencies are shown in Table 2, and FIG. 3 showslab-on-a-chip results. The AONs according to the invention designatedAON1 to AON4, AON20 to AON25 (including AONs 24.1 to 24.5) and m-h AON1have the best efficiency, with >70% of mRNA having exon 73 removed. Theeffective AONs target the 5′ end of the pre-mRNA.

TABLE 2 Efficiency of exon 73 exclusion from mRNA in HPF and HeLa cellsSEQ ID  HPF HeLa AON sequence 5′3′ NO Notes ESE73.3 82%  96%UCUCCACGGUCGCCCUUCAGCCCGCGUUCU 37 ESE73.7 80%  73%UCUCCACGGUCGCCCUUCAGCCCGC 38 AON1 67%  86% UCUCCAGGAAAGCCGAUGGGGCCC 5AON2 69%  85% AGCCCGCGUUCUCCAGGAAAGCCGA 6 AON3 67%  92%GUCGCCCUUCAGCCCGCGUUCUCCA 7 AON4 91%  83% ACGGUCGCCCUUCAGCCCGCGUU 8 AON510%   3% CCCCUGAGGGCCAGGGUCUCCACGG 9 AON6  2%   0%CAGACCAGGUGGCCCCUGAGGGCCA 10 AON7  4%   0% CCAAGGGCCAGACCAGGUGGCCCC 11AON8  0%   0% CCAGACCAGGUGGCCCCUGAGGGCC 12 AON9  0%   0%UCUCCCCAAGGGCCAGACCAGG 13 AON10  0%   0% GGAAGGCCCGGGGGGGCCCCUCUC 14AON11  6%   6% CCGGCAAGGCCGGAAGGCCCGGGG 15 AON12  0%   0%AGGCUUUCCAGGCUCCCCGGCAAG 16 AON13  0%   2% CGGGAAUACCAGGCUUUCCAGGCU 17AON14 17%  25% UGCCUGGGAGCCCGGGAAUACCA 18 AON15  8%   8%CCCACACCCCCAGCCCUGCCUGGG 19 AON16  8%   0% CCUCUCCCACACCCCCAGCCCU 20AON17  9%   9% UCUCUCCUGGCCUUCCUGCCUCU 21 AON18 11%  13%CACCCUCUCUCCUGGCCUUCCU 22 AON19  0%   7% CCAGCCUCACCCUCUCUCCUGG 23 AON2074% 100% CUCCAGGAAAGCCGAUGGGGCCC 24 AON1-1N at 3″ AON21 58%  89%UCCAGGAAAGCCGAUGGGGCCC 25 AON1-2N at 3″ AON22 64%  85%CCAGGAAAGCCGAUGGGGCCC 26 AON1-3N at 3″ AON23 64%  83%CUCCAGGAAAUCCGAUGGGGCCcu 27 AON1-N at 3′ + 1 at 5′ AON24 72%  93%UCCAGGAAAGCCGAUGGGGCCcug 28 AON1-2N at 3′ + 2 at 5′ AON24.1 32%  73%UCCAGGAAAGCCGAUGGG 39 AON24.2 50%  88% UCCAGGAAAGCCGAUGG 40 AON24.3 49% 79% UCCAGGAAAGCCGAUG 41 AON24.4 53%  86% CUCCAGGAAAGCCGAUGG 42 AON24.566%  89% UCUCCAGGAAAGCCGAUG 43 AON25 54%  92% CCAGGAAAGCCGAUGGGGCCcugc29 AON1-3N at 3′ + 3 at 5′ AON26 22%  49% AGGAAAGCCGAUGGGGCCcugcag 302N shift towards 5′ AON27 40%  37% GAAAGCCGAUGGGGCCcugcagga 314N shift towards 5′ AON28 20%  47% AAGCCGAUGGGGCCcugcaggagu 326N shift towards 5′ AON29  5%   0% GCCGAUGGGGCCcugcaggagugg 338N shift towards 5′ AON30  6%   7% GAUGGGGCCcugcaggaguggaa 3411N shift towards 5′ AON31  0%   0% UCCAGGAAAG 44 m-hAON 1 76%  91%CGUUCUCCAGGAAAGCCGAUG 35 m-hAON 2  0%  16% CCUGAGGGCCAGGGUCUCCACG 36

Two of the AONs that showed satisfactory exon skipping efficiency weretruncated by removing a varying number of nucleotides at the 3′ end inorder to avoid the occurrence undesirable G-tetrads. These AONs areshown in Table 3.

TABLE 3 Truncated versions of AON24 and AON31 SEQ ID SEQ ID NameAONs sequence NO RNA binding sequence NO length AON 24.1UCCAGGAAAGCCGAUGGG 39 CCCAUCGGCUUUCCUGG

45 18 24.2 UCCAGGAAAGCCGAUGG 40 CCAUCGGCUUUCCUGG

46 17 24.3 UCCAGGAAAGCCGAUG 41 CAUCGGCUUUCCUGG

47 16 24.4 CUCCAGGAAAGCCGAUGG 42 CCAUCGGCUUUCCUGG

48 18 24.5 UCUCCAGGAAAGCCGAUG 43 CATCGGCTTTCCTGGAGA 49 18 AON 31UCCAGGAAAG 44 CUUUCCUGG

50 10

These AONs efficiently reduced exon 73 inclusion into the COL7A1 mRNA(see Table 1), while being devoid of any sequences that are lessdesirable from a manufacturability, purification and analyticalperspective, or the chance of overall loss of function due tomultiplexing.

The functionality of Collagen VII without the exon 73 can be addressedusing several in vitro methods described in literature:

-   -   1. Protein analysis, both size and correct assembly of the        α1-collagen chains, using western blotting (Titeux et al 2010).        Of note, due to the small size of the skipped exon and the large        size of the wild type protein, the apparent difference in        protein size may not be picked-up.    -   2. Thermal stability analysis of the collagen VII homotrimer, by        using western blotting under non-reduced conditions. Wild-type        collagen VII is comprised of three α1-collagen a chains, and has        a Tm of 41° C. (Mecklenbeck et al., 2002).    -   3. Cell migration analysis using colloidal gold or scratch        assay. Compare the motility of fibroblasts and/or keratinocytes        that express wild-type collagen VII vs the truncated protein        without exon 73 (Chen et al. 2002).    -   4. Cell adhesion to various extracellular matrix components can        be assessed, e.g. to collagen IV, laminin-332, laminin-1 or        fibronectin (Chen et al. 2002).

The inventors postulate that the AONs shown to perform the best in termsof preventing, or at least reducing, exon 73 inclusion into themammalian (preferably human) COL7A1 mRNA will provide satisfactoryresults in terms of collagen VII functionality, as can be readilyassessed using the above methods from the prior art. Moreover, the AONsthat comprise no more than two (preferably no more than one, such asone) CpG will perform satisfactorily in terms of in vivo immunogenicity.Hence, the most preferred AONs of the invention are candidates fordevelopment into therapeutics, suitable for therapy in humans sufferingfrom, or at risk of suffering from, forms of dystrophic epidermolysisbullosa associated with mutations in exon 73 of the COL7A1 gene.

Example 2: Topical Delivery of Mh-AON1 Using an Ex Vivo Porcine SkinModel

Current wound management for DEB patients is mainly focused on woundcare, management of itching and pain and early diagnosis of squamouscell carcinoma. Wound care includes cleaning and sterilizing of thewounds by the means of (chloride) baths, the use of chlorhexidine as adisinfectant and other antimicrobial creams. In addition the wounds arehydrated and moisturized using hydrogels to reduce pain and itch.Finally, wound care involves bandaging with different types ofdressings/silicone foams to protect and reduce friction to the skin,prevent contamination, prevent sticking of material, absorb liquid fromthe wounds, to prevent blisters from growing in size, the blisters arepunctured and drained to decrease the pressure from within.

Topical delivery of mh-AON1 provides a couple of advantages, firstly dueto the local delivery there will be direct delivery to the target cells,keratinocytes and fibroblasts. Secondly due to the local administrationsystemic absorption will only be minor, resulting in less systemictoxicity (Wraight C J and White P J. Pharmacol Ther 2001 April;90(1):89-104). Finally, it has been shown that after topicaladministration of oligonucleotides local concentrations in the dermisand epidermis can be up to 150 (for the dermis) and 4000 (for theepidermis) times as high as after systemic administration (Metha et al.J Invest Dermatol. 2000 November; 115(5):805-12).

To investigate the topical delivery of mh-AON1 an in-house ex vivoporcine skin model was established. Porcine skin is considered to behighly similar to human skin, with equal epidermal thickness and barrierproperties of the stratum corneum. For the delivery studies, porcine exvivo skin was received, cut to a thickness between 0.8 and 1.4 mm andcultured at the air-liquid interface with the apical site air exposed.In the wounds of DEB patients the epidermis is completely separated fromthe dermis, therefore these wounds were mimicked by mechanicallyremoving the epidermis completely. To assess the skin penetration ofmh-AON1 into intact or blister-like ex vivo porcine skin, theoligonucleotide was either formulated into PBS or into a hydrogel, partof DEB standard wound care. After exposure to mh-AON1 the skin pieceswere fixed in 4% formalin, processed and embedded in paraffin forhistological assessment using hematoxylin as a counterstaining formorphology. Since the oligonucleotide was conjugated to a Cy5 label thesite of mh-AON1 could be visualized by fluorescent microscopy.

Mh-AON1 Formulated in PBS

Intact and blister-like ex vivo porcine skin pieces were incubated with25 μg of mh-AON1 formulated into PBS for 24 hours after which they wereprocessed for analysis. Results show that mh-AON1 added onto intactporcine skin pieces will not penetrate the stratum corneum (FIG. 4a-b ).However, when the mh-AON1 formulation is incubated on the blister-likeporcine skin, it was observed that the oligonucleotide had penetratedinto the dermis (FIG. 4c-f ).

Mh-AON1 Formulated into Hydrogels

For application onto patient wounds it is beneficial to incorporatemh-AON1 into an ointment or gel. Since DEB patients use hydrogels aspart of their wound care, e.g. to moisturize the wounds and therebydecrease pain and itch, it was tested whether mh-AON1 could beincorporated into a hydrogel as well. For this purpose three differenthydrogels were used: (1) Flaminal®, which is a hydrogel already used inpatient care, (2) a hypromellose hydrogel and (3) a carbomer hydrogelboth formulated in-house. All hydrogels are already commonly used inclinical settings. The hydrogel formulations were prepared with andwithout oligonucleotide, and spread on the skin pieces, 25 μg mh-AON1was formulated into 50 mg of gel for each skin piece, giving an endconcentration of 0.5 mg/ml oligonucleotide.

It was observed that mh-AON1 formulated into either Flaminal®,hypromellose or carbomer hydrogels could never penetrate the intactstratum corneum of the ex-vivo porcine skin pieces (FIG. 5 a, c, e, g).However all three hydrogels could deliver the oligonucleotide into thedermis of the blister-like porcine skin where the epidermis was removed(FIG. 5 b, d, f, h). Optimization the hydrogels is ongoing and selectionof the final formulation will be based on the dermal penetration depth,local tolerability, pH of mh-AON1 combination, stability of the mh-AON1hydrogel formulation and the release from mh-AON1 from the hydrogel.

Conclusion

DEB patients suffer greatly from their fragile skin due to blisters,wounds and ulcerations. Moreover they need constant wound care. mh-AON1was therefore assessed via the topical route of delivery. Blister-likeskin was created by removing the epidermis, including stratum corneumwhich mimics the DEB patient skin. It was demonstrated that mh-AON1formulated in either PBS or a hydrogel is able to penetrate blister-likeskin and reaches the dermis. These results support that topicaladministration to the patient's skin wounds is a feasible approach todeliver mh-AON1 to the target cells in the skin. Moreover, thesefindings support that a formulation resembling EB standard of care seemssuitable in delivery of mh-AON1.

Example 3: Efficacy Testing at the mRNA Level

Two different cell types were used to assess the effectivity of mh-AON1:(1) HeLa and (2) skin derived human primary fibroblasts (HPF) fromhealthy individuals. Both cell types express COL7A1 mRNA and produce thecollagen type VII protein. mh-AON1 as disclosed herein has been designedto exclude exon 73 from the COL7A1 mRNA, and thus exclude mutations fromthe transcript. Since mh-AON1 targets the splicing process, the mostdirect measurable outcome of efficacy is the profiling andquantification of COL7A1 transcripts (wild type and Δ73) with andwithout the addition of mh-AON1.

Profiling and Quantification of COL7A1 mRNA Level Through PolymeraseChain Reaction (PCR)

PCR is a straightforward technology which enables the logarithmicamplification of a specific DNA (cDNA) sequence. COL7A1sequence-specific primers, flanking exon 73, were used to perform thePCR reaction. Afterwards the products formed were visualized using labon a chips technology that allows discrimination of different fragmentlength products and the quantitative analysis based on yield.

For exon 73 skip experiments, HPF and HeLa cells were transfected withmh-AON1 at a concentration of 100 nM using polyethyleneimine (Poly I:C)as a transfection vehicle. 24 or 40 hours post transfection, the cellswere harvested, whole mRNA isolated, cDNA synthesized and a PCRperformed using COL7A1 specific primers, one in exon 69 and one in exon74. As a negative control a scrambled (SCRM) version of the mh-AON1oligonucleotide was taken along.

Results show that treatment with mh-AON1 leads to efficient exclusion ofexon 73 from the COL7A1 mRNA compared to SCRM treated cells (FIG. 6) asdetermined by PCR. Furthermore, the level of wild type mRNA in untreatedcells was comparable to the level of total COL7A1 mRNA in treated cells.Since the PCR/bioanalyzer method is informative but not absolutequantitative, these initial findings were followed up by using dropletdigital PCR assays which offer highly accurate and absolutequantification of nucleic acid fragments.

Profiling and Quantification of COL7A1 mRNA Transcripts with DropletDigital PCR

Droplet digital PCR (ddPCR) provides a highly accurate and absolutequantification of nucleic acids through the partition of the PCR sampleinto thousands of droplets. The COL7A1 mRNA/cDNA PCR input was adjustedin such a way that each droplet contains either one or none COL7A1 cDNAmolecule. To allow detection of the template, a probe specific for wildtype or Δ73 COL7A1, was added to the PCR mix. The location of theseprobes are depicted in FIG. 7. One of the probes is specific for thewild type product, while the other probe is specific only for the Δ73COL7A1 product. This probe upon binding to the template gets hydrolyzedand become fluorescent, so that after PCR amplification is performed,the fluorescent droplets containing the target sequence can be counted.Using Poisson statistical analysis of the numbers of positive andnegative droplets, absolute quantitation of wild type or Δ73 COL7A1 mRNAmolecules in the sample can be calculated.

HeLa cells were transfected with either 50, 100 or 200 nM mh-AON1 toestablish a dose-response profile for mh-AON1. Results from 24 h aftertransfection show that treatment with mh-AON1 results in both COL7A1wild type transcripts and Δ exon 73 transcripts. These resultscorroborate the observations seen with PCR. The dose of 50 nM alreadygives almost maximum effect after 24 h. After 40 h a small increase inthe % of Δ exon 73 transcripts was observed for the 50 nM and 200 nMtransfection (FIG. 8).

Example 4: In Vitro Immunogenicity Tests

Oligonucleotides have the potential to cause activation of patternrecognition receptors (PRR) of the vertebrate innate immune system. Thebest studied family of PRR receptors are the toll-like receptors (TLRs).TLRs are a class of proteins that play a key role in the innate immunesystem. They are single, membrane-spanning, non-catalytic receptors thatare usually expressed in macrophages and dendritic cells that recognizestructurally-conserved molecules derived from microbes. TLRs that areactivated by different types of nucleic acids are those located onendosomes: TLR 3 (recognizes double stranded RNA); TLR7/8 (recognizesdouble and single stranded RNA); and TLR9 (recognizes CpG-DNA).

Upon recognition of these components by the PRRs, a specific‘antimicrobial’ immune response is triggered. TLR activation results inthe activation of nuclear factor kappa-light-chain-enhancer of activatedB cells (NE-κB), Interferon regulatory factor 3 (IRF-3) and activatorprotein 1 (AP-1). Activation of AP-1, IRF-3 and NE-κB results in theproduction of inflammatory cytokines, type-I interferons and othermediators of the innate immune response. These processes not onlytrigger immediate host defensive responses such as inflammation, butalso prime and orchestrate antigen-specific adaptive immune responses.

In vitro exposure of primary human peripheral blood mononuclear cells(PBMC) to mh-AON1 was used to assess (systemic) drug-specific immuneresponses and immunotoxicity. The in vitro assay using PBMC is anestablished preclinical test using the production of (inflammatory)cytokines as surrogate marker for systemic immune responses. The PBMCassay enables prediction of tolerability as a factor of theimmunogenicity and allergenicity potential of investigational compounds,and could enable an estimation of a safe dosing range for thesecompounds.

For the studies of mh-AON1, in-house isolated PBMC were used, acquiredfrom buffy coats of healthy blood bank donors. Production of the keypro-inflammatory cytokines in the culture supernatant was assessed after24 h of stimulation with mh-AON1 at concentrations ranging from 10 nM to1 μM. In addition, the Ramos-Blue (Invivogen, human B cells) reportercell line with chromosomal integration of a secreted embryonic alkalinephosphatase reporter construct inducible by NE-κB and/or AP-1 was usedto assess general PPR-mediated immune activation by mh-AON1 andAON73.24.5. Ramos-Blue cells express the relevant set of TLRs,including: TLR3, −7/8 and −9. Activation NE-κB and/or AP-1 was measuredafter 24 h of stimulation with mh-AON1 or AON73.25.4 at concentrationsranging from 10 nM to 1 μM. Moreover, the viability of the PBMC andRamos-Blue after treatment with mh-AON1 was analyzed by measuring thefluorescent resorufin in the culture supernatant to assess potentialcytoxic effect of mh-AON1. Viable cells convert the non-fluorescentresazurin into fluorescent resorufin.

Results in Human PBMC

Stimulation of human PBMC with the positive controls LPS (TLR4 agonist)and R848 (TLR7/8 agonist) resulted in significantly increasedconcentrations of all measured cytokines, except IL-3, in the culturesupernatant. Moreover, stimulation with CpG DNA (TLR9 agonist) or Poly(I:C) (TLR3 agonist) induced a similar pattern of cytokines, although toa lesser extent. A Heat map depicting the significance levels ofcytokine concentrations in culture supernatant after stimulation withmh-AON1 or the positive controls compared to saline-treated human PBMCis shown in FIG. 9a . Importantly, stimulation of human PBMC withmh-AON1 concentrations ranging from 10 nM to 1 μM did not results inincreased concentrations of any of the measured cytokines in the culturesupernatant, with the exception of IFN-α2 at the lowest concentrationmh-AON1 (FIG. 9a ). However, since the increase in concentration ofIFN-α2 in the supernatant after stimulation with mh-AON1 is not dosedependent, this was considered as an experimental outlier or technicalerror (FIG. 9b ). Finally, there were no signs of cytotoxicity 24 hafter treatment with mh-AON1 (FIG. 9c ). In contrast, there was a slightincrease in viability observed after treatment with R848, or 10 nM and100 nM mh-AON1 suggesting enhanced cell survival, increased cellmetabolism or even increased proliferation/differentiation.

Results in Ramos-Blue Cells

Results of the immunogenicity assay carried out in the human Ramos Bluecell line showed no activation of NE-κB and/or AP-1 after 24 h treatmentwith mh-AON1 or AON73.24.5 at concentrations ranging from 10 nM to 1 μM(FIG. 10a ). In contrast, the positive controls Poly(I:C) (1 μg/ml), CpG(10 μg/ml) and R848 (1 μM) did induce activation of NE-κB and/or AP-1.LPS had no effect, since TLR4 is not expressed on Ramos-Blue. Moreover,there were no signs of cytotoxicity 24 h after treatment with MH-AON1(FIG. 10b ) confirming the results obtained in human PBMC.

It will be understood that the invention is described above by way ofexample only and modifications may be made whilst remaining within thescope and spirit of the invention.

The invention claimed is:
 1. An antisense oligoribonucleotide capable of preventing or reducing exon 73 inclusion into a human collagen type VII alpha 1 chain (COL7A1) mRNA when the mRNA is produced by splicing from a pre-mRNA in a human cell, wherein the oligoribonucleotide comprises a nucleotide sequence having a length of between 12 and 24 nucleotides that is at least 95% complementary to a target nucleotide sequence in a COL7A1 pre-mRNA, wherein the target nucleotide sequence is fully complementary to SEQ ID NO: 5, 24, 25, 26, 27, 28, 39, 40, 41, 42, 43, 29, or 35, and wherein the oligoribonucleotide comprises at least one nucleotide analogue or equivalent.
 2. The antisense oligoribonucleotide of claim 1, wherein the oligoribonucleotide can anneal to the target nucleotide sequence in a COL7A1 pre-RNA molecule under physiological conditions, thereby facilitating skipping of exon
 73. 3. The antisense oligoribonucleotide of claim 1, wherein the target nucleotide sequence is fully complementary to SEQ ID NO:
 35. 4. The antisense oligoribonucleotide of claim 1, wherein (a) the oligoribonucleotide has no more than two CpG sequences; (b) the oligoribonucleotide has a non-natural internucleoside linkage; and/or (c) the nucleotide analogue or equivalent comprises (i) a modified ribose moiety comprising a lower 2′-O-alkyl modification, a 2′-O-alkyl-O-alkyl modification, or a 2′-methoxyethoxy modification; or (ii) a locked nucleic acid (LNA), in which the 2′-carbon atom is linked to the 3′ or 4′ carbon atom of the ribose ring, thereby forming a bicyclic ribose moiety.
 5. The antisense oligoribonucleotide of claim 4, wherein (a) the oligoribonucleotide has no more than one CpG sequence; (b) the oligoribonucleotide has a length of between 16 and 23 nucleotides; (c) the oligoribonucleotide has a phosphorothioate internucleoside linkage; and/or (d) the nucleotide analogue or equivalent comprises (i) a modified ribose moiety comprising a 2′-O-methyl modification; or (ii) an LNA, in which the 2′-carbon atom is linked to the 4′ carbon atom of the ribose ring by a 2′-O, 4′-C-ethylene bridge.
 6. The antisense oligoribonucleotide of claim 5, wherein (a) all the internucleoside linkages of the oligoribonucleotide are phosphorothioate linkages; and/or (b) all the nucleotides of the oligoribonucleotide are nucleotide analogues or equivalents comprising (i) a modified ribose moiety comprising a 2′-O-methyl modification; or (ii) an LNA, in which the 2′-carbon atom is linked to the 3′ or 4′ carbon atom of the ribose ring.
 7. The antisense oligoribonucleotide of claim 1, wherein the oligoribonucleotide is capable of reducing exon 73 inclusion in a HeLa cell, or a sample derived therefrom, by more than 70%.
 8. The antisense oligoribonucleotide of claim 7, wherein the oligoribonucleotide is capable of reducing exon 73 inclusion in a HeLa cell, or a sample derived therefrom, by more than 80%.
 9. The antisense oligoribonucleotide of claim 8, wherein the oligoribonucleotide is capable of reducing exon 73 inclusion in a HeLa cell, or a sample derived therefrom, by more than 90%.
 10. A composition comprising the antisense oligoribonucleotide of claim 1 and one or more of a carrier, excipient, stabilizer, transfection agent, diluent, gelling agent, and buffer.
 11. The composition of claim 10, which is a pharmaceutical composition for use in a human suffering from, or at risk of suffering from, forms of dystrophic epidermolysis bullosa associated with mutations in exon 73 of the COL7A1 gene.
 12. A method for preventing or reducing exon 73 inclusion into a human COL7A1 mRNA when said mRNA is produced by splicing from an RNA transcript in a human cell, the method comprising providing to the cell the antisense oligoribonucleotide of claim 1, under conditions conducive to uptake of the oligoribonucleotide by the cell, and allowing splicing to take place.
 13. The method of claim 12, wherein the antisense oligoribonucleotide comprises the nucleotide sequence of SEQ ID NO:
 35. 14. The method of claim 12, wherein the antisense oligoribonucleotide consists of the nucleotide sequence of SEQ ID NO:
 35. 15. The method of claim 14, wherein (a) the oligoribonucleotide has a phosphorothioate internucleoside linkage; and/or (b) the nucleotide analogue or equivalent comprises (i) a modified ribose moiety comprising a 2′-O-methyl modification; or (ii) an LNA, in which the 2′-carbon atom is linked to the 3′ or 4′ carbon atom of the ribose ring. 